The most effective measure to prevent many diseases is the mass immunization with vaccines. Since medical science has come to understand the principles of viral theory and its importance to the transmission of diseases, the need to break the viral or bacterial transmission chain from host to host has become well-established. There are wide varieties of methodologies accepted by medical science to break the chain depending on the requirements of the situation. The most stringent protocols include: sterilization, disinfection, and sanitization utilizing heat chemicals and/or ionizing radiation.
Barriers are another common protocol and can be as simple as establishing an imaginary boundary where one side of the boundary is kept clean and the other is defined as contaminated. Any object being transferred from the clean to the contaminated side of the boundary is not returned to the clean side without being disinfected, sanitized, or sterilized. A typical example of this type of protocol is within the medical surgical fields. The surface of the operating table is defined as the boundary. Any item that is dropped below the surface of the operating table is immediately defined as contaminated. This includes surgical implements or the surgeon's hands.
With needle injection devices there are two common protocols both of which start from the premise that a used syringe is, by definition, contaminated. The first, which is commonly used in dentistry, uses syringes and sometimes needles that are sterilized after each use. The second is more commonly used in general medicine in the U.S. and other developed countries. This is the disposable syringe and needle assembly. Because of the low cost of production typically—less than $0.10 per syringe assembly—this protocol is well-accepted.
Jet injector systems on the other hand continue to be characterized by relatively high cost per injection ($1.00 or more) when the syringe portion of the injector is discarded with each use. Additionally, there is the challenge in developing countries where lack of understanding of viral theory and/or a general hoarding mentality discourages following generally accepted protocols within all aspects of health and hygiene. With the identification of blood-borne pathogens like HIV, Hepatitis B, Hepatitis C and others, the need to follow proper protocols becomes more critical.
In the past, jet injectors such as Ped-O-Jet®, Ammo-Jet®, and similar mass campaign jet injectors were brought to health care systems. Such injectors had no provision for preventing the transfer of blood-borne pathogens except through the complicated disassembly and disinfecting process. In mass immunization campaigns these types of injector systems fell out of favor starting in the mid and late 1980's when it was determined that bodily fluids are easily transmitted from one patient to another.
To eliminate the possible transmission of blood-borne pathogens between individuals, disposable or partially disposable jet injector systems were developed. Bio-Jet®, J-Tip®, and others characterize this type of jet injector. General acceptance of these units is limited by relatively high direct costs, even in developed countries like the United States. The standard paradigm of breaking the contamination transmission chain has been addressed by either syringe disposal or designing the syringe so it can easily be decontaminated. Currently, there exists a steadily growing danger of the epidemic diseases (AIDS, hepatitis, tuberculosis and other viral diseases transferred through blood) being transmitted between individuals through the use of needleless injectors.
The traditional needleless injectors comprise the basic design, a housing with an inner power unit, a medication unit, and a nozzle. The function of the power unit pumps the medication into an under-plunger cavity of the medication unit chamber and to expel the medication through the nozzle.
At the initial stage of needleless injector development, when no check valves were used as a control for the functioning of the medication chamber, a method to prevent foreign particles from entering the injector nozzle was to use a sealed nozzle cap. Such cap was limited by the filling of the medication chamber with medication and could not guarantee contamination prevention.
Another approach to the contamination prevention problem has been the use of a disposable, low cost, one-shot nozzle assembly for jet injectors. The nozzle assembly comprises a two-piece molded device incorporating a generally cylindrical nozzle body having a central longitudinal bore of a predefined diameter, extending from a proximal end of the nozzle towards its distal end, terminating in a conical portion of the nozzle. A very small diameter jet-forming bore is formed at the apex of the conical portion of the bore in general. The disadvantage of this device is its lower efficiency (i.e., low vaccination rate) because of poor flow due to the conical design. Moreover, a plastic nozzle element also increases the vaccination cost.
A typical jet injector design has additional drawbacks. Even in the practice of using a protective cap, there is a possibility of infection transfer from one person to another by means of fluids (blood, lymph, medication) reflected from the skin surface during injection (“back splash”) that may get on the nozzle and be transferred from one patient to the next. The protective cap can be a one-shot cap, including the injection nozzle. A purpose of this device is to prevent the multiple use of a cap with a nozzle. This is achieved through the removal, replacement, and/or destruction of the cap at the later stage of the injection. However, cross-contamination continues to be problematic because in the injection stage, the contaminated matter can be transferred through the nozzle to inside the injector such as, for example, into the cavity and be transmitted to a new patient through a new cap and nozzle.
With all the known devices, there is no guarantee that the minimum safety requirements for cross-contamination prevention, as recently introduced (Glenn Austin et al., Gross Contamination Testing of Vaccine Jet Injectors, A Preliminary Report, PATH, Seattle, Wash., 98109), will be achieved. Other studies indicate a very dangerous situation. For example, Russian and Brazilian studies have shown unfavorable data in up to 1.0% of the subjects studied—a level of risk far too great to ignore.
When jet injectors were introduced in the 1940's, they were popular for needle phobic patients or small veined patients. Improvements permitted jet injectors to administer hundreds of millions of vaccinations that saved countless lives. However, when the discovery of pathogen transfer occurred, jet injectors fell out of favor to such an extent that the WHO and the U.S. Department of Defense no longer recommended jet injector.
For example, in the mid-1980's an outbreak of Hepatitis B was caused by use of one high workload injector in a weight loss clinic. See, Canter et al., An Outbreak of Hepatitis B Associated With Jet Injections In A Weight Loss Clinic, Arch. Intern. Med., 150:1923-1927 (1990).
Present parenteral injection technology has recently been deemed by the World Health Organization (WHO) to be incompatible with their requirements for the planned Global Programme of Vaccination and Immunization (GPV) initiatives. It is estimated that 6 additional parenteral vaccines will be recommended for childhood vaccination by the year 2005, requiring a total of 3.6 billion immunization injections per year. The total number of parenteral injections, including injected drugs as well as vaccines, will be roughly ten times this number. This is in addition to the hundreds of millions needed in military induction centers, epidemic situations, worldwide immunizations, and veterinary uses. Major health care providers such as UNICEF, the WHO and CDC have recently confirmed that a radical new technology is required that can be used by personnel with minimal training and that is safer, more convenient, and more comfortable than the syringe and needle. (Jodar L., Aguado T., Lloyd J. and Lambert P-H, (1998) Revolutionizing Immunizations Gen. Eng. News 18, p. 6.)
In other words, what used to be a continent wide life saver, became an undesirable product. The present invention solves problems associated with pathogen transfer and solves many problems associated with the high costs of disposable units.
Coupled with this was that accidental discharge of the medication sometimes occurred. Premature injection could result in an incomplete injection or an injection in the improper situs.
Accordingly, there is a need in the art of needleless injection devices to solve the problem of cross-contamination during mass vaccinations. More particularly, there is a need for a protector designed for the nozzle head of needleless injectors, which halts “back splash” contamination, and which is low enough in cost to ensure its practical application as a disposable unit even for mass vaccinations. There is also a need to ensure that the incidence of premature discharge is reduced or eliminated.